Thermoelectric power, Hall effect, and mobility of n-type ${\mathrm{BaTiO}}_3$

The resistivity and the Hall and Seebeck effects of polycrystalline n-type ${\mathrm{Ba}}_{0.996}{\mathrm{Y}}_{0.004}{\mathrm{TiO}}_3$ and undoped, reduced single crystal ${\mathrm{BaTiO}}_3$ were studied in the 100–300 K interval. Both Hall coefficient and resistivity showed similar temperature activated dependence for the single crystal in the rhombohedral phase and for the polycrystal in the rhombohedral and orthorhombic phases. Low-temperature Hall mobility in the ${\mathrm{BaTiO}}_3$ single crystal decreased from $12{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at 120 K to $2{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at 220 K, implying a phonon scattering of charge carriers. The temperature dependence of the Hall mobility of the polycrystal showed a weak temperature dependence in the 100–220 K range with a maximum of $1.2\pm 0.3{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at 170 K, probably indicating a transition from ionized impurity scattering at low temperature to a phonon scattering at higher temperatures. Temperature dependence of thermopower and Hall coefficient confirmed that the increase in conductivity of the single crystal below 200 K was caused by an increase in the concentration of the charge carriers. The results suggest that below 300 K, electron transport in ${\mathrm{BaTiO}}_3$ occurs via the conduction band rather than by a small polaron hopping.